1. Field of the Invention
The present invention relates to a light emitting device having a light emitting element sealed by a sealing member made of, for example, glass.
2. Description of the Related Art
It is well known that the light emitting device, which blends the light emitted from a light emitting diode (LED) element with the wavelength conversion light emitted by a phosphor pumped by the aforementioned light to obtain white light, has been adopted in practical applications.
It is well known in the related art that the light emitting device of this type includes an element mounting substrate, an LED element mounted on the element mounting substrate, and a sealing member that seals the LED element (for example, see: Patent Reference 1).
The element mounting substrate includes a substrate main body and a circuit pattern. The substrate main body is made of a ceramic material, and the circuit pattern is formed by metallizing on the outer/back surfaces of the substrate main body.
The LED element is a blue light LED element that emits blue light. It is mounted on the element mounting side of the element mounting substrate, and it is connected with the circuit pattern.
The sealing member is made of a glass containing a phosphor that emits yellow light when pumped by the blue light emitted from the LED element.
For the light emitting device that has the aforementioned constitution, the blue light emitted from the LED element and the yellow wavelength conversion light emitted from the phosphor pumped by the blue light are blended with each other to form white light.
Patent Reference 1: JP-A-2008-71837
However, the light emitting device described in Patent Reference 1 has some problems. That is, a portion of the light is absorbed by the substrate main body and the circuit pattern of the element mounting substrate, and loss in light takes place as the light goes through the substrate main body, decreasing the light output efficiency, which is undesirable. For example, when the surface of the circuit pattern is treated by plating of gold (Au), about 60% of the light quantity among the light quantity of the blue light emitted from the LED element is absorbed. When the circuit pattern is made of tungsten (W) and chromium (Cr), light absorption over that of Au takes place easily. Even when the material of the substrate main body is made of aluminum nitride (AlN) or silicon (Si), the light absorption is still too significant to be neglected.